Methods for the epoxidation of an olefin with hydrogen peroxide using a water soluble manganese complex as epoxidation catalyst are known from D. E. De Vos et al., Tetrahedron Letters 39 (1998) 3221-3224 and from U.S. Pat. No. 5,329,024.
WO 2010/012360 discloses epoxidation of allyl chloride in an aqueous reaction medium with a water soluble manganese complex as epoxidation catalyst. The reaction product epichlorohydrin forms an organic phase and a settler may be used to optimize gravitational separation of the epichlorohydrin. A membrane unit may be used to recycle the aqueous reaction medium with reduced loss of catalyst.
WO 2011/107188 discloses use of a loop reactor for epoxidation with this catalyst in a multiphasic reaction mixture comprising an organic phase and an aqueous phase. Reaction mixture withdrawn from the loop reactor is separated into an aqueous phase and an organic phase in a settler and aqueous phase is recycled to the loop reactor.
WO 2012/175182 teaches that the manganese complex cannot be successfully recycled with the separated aqueous phase because it deactivates during phase separation when the aqueous phase is not intensively mixed with the organic phase. The document further teaches that such deactivation can be avoided by lowering the pH of the aqueous phase before carrying out phase separation. However, the catalyst has low catalytic activity for epoxidation at the low pH needed for stabilizing the catalyst and the pH has to be raised again for efficiently reusing the catalyst in the epoxidation reaction. The catalyst recycling proposed in WO 2012/175182 therefore leads to salt formation from the acid and the base which have to be added for lowering and increasing the pH of the aqueous phase.